The invention relates to a gas transfer device with a specifically structured membrane, wherein thanks to its structuring the membrane permits particularly effective gas exchange, in particular between a liquid phase and a gaseous phase.
Gas transfer devices are used in many fields of technology. Such devices are either gassing or degassing devices, in which one or more gases pass from one medium into another, or gas exchange devices which permit mutual exchange of one or more gases between two media. Gas transfer devices are used, for example, in chemical process engineering, where they serve to supply gases for gas/liquid or gas/solid reactions. They may, however, also be used for gas separation or gas purification, by a gas not being introduced, but instead stripped out of a gas mixture or another reaction mixture.
Gas transfer devices are moreover likewise used in biotechnology and medicine. Their most important place of use in biotechnology is use in culturing reactors. Gas transfer devices are used to supply cell cultures in a specific and controlled manner with the gases necessary for a certain culture or excreted gases are removed from the nutrient medium. Gas transfer devices are also used in medicine. In this case, the most important intended use is to oxygenate the blood while simultaneously removing carbon dioxide from the blood. Such measures are required, for example, in diverse surgical operations and in the treatment of various lung diseases.
Causing as they do 9 million deaths per year, lung diseases are in third place in the WHO's cause of death statistics. Lung transplantation is currently the only therapeutic option with long-term effectiveness for patients with end-stage functional lung disease. There is at present no other medical solution for the long-lasting replacement of lung function. There is therefore in particular a significant requirement for long-lasting, artificial lung replacement methods which can be used in patients with chronic lung disease who cannot be considered for lung transplantation. There is moreover likewise a requirement for lung replacement devices which can be used in patients awaiting lung transplantation. Waiting times are currently so long that some 80% of patients die before receiving the lung transplantation which is medically indicated. Suitable lung replacement devices which can be used over extended periods could be of assistance here.
Gasifying devices were developed for such purposes as long ago as the 1950s. These devices, known as oxygenators, i.e. oxygen-gasifying devices, have since undergone continuous development and their functionality is still today being further improved.
The prototype of such an oxygenator was a film oxygenator in which blood conveyed by a roller pump through screens was oxygenated in an almost pure oxygen environment. However, large-area direct contact with oxygen led to denaturation of plasma proteins, a decisive drawback to the use of the film oxygenator.
The “bubble” oxygenator was then developed, blood being oxygenated with gas bubbles in a column of blood. The level of saturation is adjusted by varying the gas flow. Gas exchange here proceeds directly on the surface of the gas bubbles. The most serious problem of the bubble oxygenator was and remains the foaming of the blood which occurs during oxygenation, which can lead to microembolisms in the body. Subsequent defoaming methods are therefore required, making this method complex and costly. Examples of bubble-type oxygenators are described inter alia in DE 22 08 868, DE 23 14 644, DE 23 32 445 and DE 30 01 018.
Shortly after the bubble oxygenator was developed, a membrane oxygenator was used for the first time as long ago as 1956. In the membrane oxygenator, the gas phase is separated from the blood phase by a membrane. Gas exchange proceeds at the gas-permeable membrane primarily by diffusion due to partial pressure differences between the gases involved. The membranes may here take the form of flat membranes or of capillary or fibre membranes. Two types of membrane oxygenators from the more recent prior art are described, for example, in U.S. Pat. No. 5,137,531 and U.S. Pat. No. 6,682,698. One general disadvantage of membrane oxygenators which operate by diffusion is, however, that large membrane areas must be provided in order to achieve effective mass exchange between blood and oxygen in a specific time. Diffusion through the membrane may here by influenced by increasing oxygen pressure or by modifying the flow characteristics of the blood. It is, however, fundamentally really difficult to strike a compromise between potential blood damage, tendency towards thrombosis and effective gas exchange.
While very good diffusion may indeed be achieved in the fibre membrane oxygenators which are predominantly in use today thanks to the large total surface area of the membrane, a drawback for this oxygenator is the costly and complex manufacture of the fibres. A further disadvantage of currently used oxygenators is their only very short useful life. A prior art oxygenator may accordingly be used for only a few days, for at most up to a month. Long-term use, as would in particular be desirable for patients with chronic lung failure, cannot however be carried out satisfactorily.
The disadvantages stated by way of example for the oxygenators used in medicine occur likewise in gas transfer devices which are used for process engineering purposes in chemistry and biotechnology.